Rom-com recipe lacks flavor

You’d think by now Hollywood would have romantic comedies down to a cell-phone app any studio exec could access.

Cute couple? Check.

Romantic location? Check.

“Obstacles” to romance? Yup.

“Wacky,” witty friends of each young lover? Check and check.

But if it was just a formula, then you could hire any hack — say, the chap who did “Ghostrider,” to turn Kristen Bell into America’s new sweetheart in “When in Rome.”

Bell, a petite, pretty blonde, may or may not have the Meg Ryan-Julia Roberts-Sandra Bullock goods.

“When in Rome,” a leaden variation on that rom-com recipe, fails utterly to make her case.

It’s got cute Kristen playing Beth, a curator at the Guggenheim. She has a quirky staff. Note to whoever cast Kate Micucci. “Funny looking” is no substitute for “funny.”

And Beth has a younger sister (Alexis Dziena, the only actress tinier than Bell) getting married in Rome. At the wedding, Beth is ready to be “open” to love, as her dad (Don Johnson) suggests. And devil-may-care sports reporter Nick (Josh Duhamel) fills that bill. But he may be a womanizer, leading Beth to a drunken dip in the Fontana di Amore, where she steals a few coins and sets our plot in motion.

Those coins were wishes, and the men who tossed them — a sausage magnate played by Danny DeVito (”Encased meat is my life’s work”), a screwball magician (Jon Heder, funny), a demented Italian artist (Will Arnett) and a self-absorbed “model” played by Dax Shepard (”I don’t know whether to look at my own reflection or you. That’s how beautiful you are!”) — are instantly smitten.

Can Beth shed her unwanted beaus and tumble for Mr. Right? Is Mr. Right pursuing her of his own free will, or did he toss a coin, too?

One cute scene — Nick and Beth date in a blackout restaurant, where diners can’t see each other or their food. We watch that train wreck through night-vision goggles. Duhamel (the “Transformers” movies) has a light touch — glibbing through scenes with his cut-rate and generally unamusing sidekicks.